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A 3D dynamic model has been developed to investigate the dynamic response of a finger-follower cam system by considering the interaction between valve train and camshaft. The torsional moments being different for each cam cause the torsional vibrations of the camshaft. The resulting speed fluctuations of the cam affect the dynamics of other valve train components including the ultimate valve motion.

To better represent the critical parts of the valve train, special attention was given to the cam and follower and to valve springs. The cam and follower are treated as a force contact relation so parts can separate and impact again. The valve springs are now treated as flexible bodies and important mass effects and coil contact events are captured during the simulation. The mass effects are associated with spring surge that occurs at high speed. Coil contact occurs when the individual coil in the spring collides.

One bank of a V6 engine with overhead twin cams is modeled in this study. The complete flexible multi-body model of the valve train includes flexible camshafts, valves, springs and rocker arms. The multi-body dynamic code, DADS, is used in this work. The complete model contained a total of 38 flexible bodies, each having multiple modes to represent flexibility. In Addition to the cam and follower, there are contact force elements used throughout the model, including the rocker pallet to valve tip and valve to valve seat. Hydrodynamic bearings are modeled to represent the nonlinear effects of oil film in the journal bearings of camshaft. Another feature of the model is the combustion force acting on the valves.